The present invention generally relates to a process for vulcanization of elastomer products made, for example, of synthetic rubber, elastomeric plastics, etc., and more particularly, to an improved process for vulcanization of elastomer products, especially pneumatic tires and the like.
Conventionally, in the vulcanization of pneumatic tires for motor vehicles, etc., there have generally been adopted a steam vulcanizing system which employs steam as a heating medium, and a hot water vulcanizing system which employs hot water as a heating medium. In any of the above systems, application of predetermined degrees of temperature and pressure is essential, but, while the supply of pressure is indispensable up to the termination of the heating process, continuous supply of heat amount is not substantially required by providing a sufficient heat insulation or by replenishing heat amount equivalent to the heat amount radiated, if a proper amount of heat is supplied at the initial stage of the heating process to attain the standard temperature necessary for the vulcanization.
However, in the known steam vulcanizing system as described above, partly due to the employment of saturated steam, it is necessary to continuously supply the steam at predetermined degrees of temperature and pressure up to the termination of the heating process, even after the tire to be processed has reached the standard temperature whereat the supply of heat is not required so much. Meanwhile, in the hot water vulcanizing system referred to above, since the temperature and pressure are independently changeable, even if the pressure has to be continuously supplied up to the completion of the heating step, supply of heat amount for maintaining the temperature is assumed to become unnecessary, after the tire to be processed has attained the standard temperature. However, owing to a large specific heat of water, when the temperature of hot water is lowered upon suspension of the supply of heat, the temperature of the tire is also undesirably lowered due to absorption of the heat amount by water, and thus, it is required, after all, to continuously supply hot water at predetermined degrees of temperature and pressure up to the termination of the heating process. Since the known processes as described above are of course very wasteful from the viewpoint of savings of resources, there has recently been attempted to employ a combination of steam or hot water and gas in the heating process for vulcanization of tires. The gas referred to above, however, is one produced by the so-called burning furnace system in which exhaust gas (mainly composed of nitrogen) obtained by subjecting raw gas to complete combustion in a burning furnace, is cooled down close to room temperature and pressurized by a compressor, through employment of propane gas, butane gas, city gas, etc. associated with petroleum as the raw gas. Therefore, not only the energy cost is high, thus going against the requirements for savings of resources, but control of ratio of air for burning is not easy due to unsteady fuel gas compositions, while construction of an arrangement therefore with a small burden is difficult owing to the presence of carbonic acid, nitric acid, etc. brought about by impurities such as carbon dioxides, nitrogen oxides, etc., and thus, for example, effective utilization of the used inactive or inert gas discharged is not readily effected, with a consequent high installation cost, while there is a possibility that toxic gases such as carbon monoxide, and nitrogen oxides which may give rise to public pollution, may be developed.